This invention relates to the manufacture of a brazed assembly to a selected geometry, the assembly including an environmental resistant coating and at least one wear resistant surface portion; and, more particularly to an assembly for operation with cooperating, contacting members in a high temperature oxidizing environment.
Various components for use in power generating apparatus such as turbine engines are manufactured by joining, such as by brazing, a plurality of members into a final assembly. Examples of such components in a turbine engine include turbine nozzle segments, shrouds, shroud hangers, combustor components, and seal components, among others, some of which are coated with an environmental resistant coating. Such components cooperate closely, frequently in a sliding or rubbing relationship, with an adjacent component of the apparatus, for example a turbine nozzle and a shroud hanger. Therefore, selected surfaces of one or more of the cooperating members have been provided with a wear resistant material at an interface between members. In addition, to enable such components to be assembled to a selected, design geometry for the apparatus, sometimes called a xe2x80x9cstack-upxe2x80x9d limit range, such selected surfaces are shaped, such as by machining. Although such members generally are made of a high temperature alloy based on at least one of Fe, Ni, and Co, operation in a strenuous oxidizing environment has required that such members include at least an environmental resistant surface coating.
The provision of a component comprising a plurality of joined members including a wear resistant surface, an environmentally resistant coating, and an interface surface that cooperates with an adjacent component interface within a xe2x80x9cstack-upxe2x80x9d geometry limit has resulted in a relatively complex manufacturing sequence. For example, in the manufacture of a gas turbine engine high pressure turbine nozzle, it has been a practice first to join a plurality of members of the nozzle into an assembly by brazing, then to machine selected interface surfaces to a required geometry. An environmental resistant coating, for example a diffusion aluminide coating of a type widely used in the gas turbine engine art, is applied at an elevated temperature to the assembled and machined component. Thereafter, to prepare a selected surface, which now includes a protective coating, for a wear resistant material, the selected, coated surface is machined to remove the coating from the selected surface. This is conducted to facilitate the wear resistant material in bonding with the selected surface because it is difficult to bond the wear resistant material to a protective coating like an aluminide. A wear resistant coating then is applied such as by plasma spraying or by bonding a wear resistant preform to the surface thus prepared. The wear resistant coating is machined to a final geometry to provide an assembled geometry within the xe2x80x9cstack-upxe2x80x9d limit range. This relatively complex series of manufacturing steps is relatively costly and is in need of simplification while providing the same results and geometry range limits.
The present invention, in one form, provides a method for making an article from a plurality of members brazed together, the article including an environmental resistant surface coating and a wear resistant surface portion. The method includes the steps, prior to brazing, of first assembling together a discrete wear resistant material preform including a first brazing alloy having a brazing temperature range, and the plurality of members to be brazed, with a second brazing alloy having substantially the same brazing temperature range. Then that assembly is brazed in the brazing temperature range that concurrently brazes the plurality of members and the discrete wear resistant preform to the assembly to provide an article preform. The article preform, including at least the wear resistant material, is machined to a selected geometry. Thereafter, the machined article is coated with an environmental resistant coating.